This invention relates generally to cooktops and more particularly, to controlling operation of a cooktop based on cooktop temperature.
The term cooktop as, used herein refers to a cooking system that comprises at least one electric heating element or heater. A cooktop system can be a stand-alone unit that is mounted, for example, on a kitchen countertop. A cooktop system also can be integrated with an oven to form a range. Ranges including cooktop systems and stand alone cooktop systems are commercially available from the GE Appliances business, Louisville, Ky., of General Electric Company.
Cooktop systems typically have a generally planar glass-ceramic cooking surface with heating units located just below the cooking surface. Each heating unit, or heater, is operable at various power levels. Prior to operation, a user typically positions a pot or pan containing food on the glass cooking surface over a heater to be operated and selects, via a user interface, a desired power level for the heating element. The cooktop system responds by supplying power to the selected heating element in accordance with the user selected power level. For example, for a lower power level setting (e.g., a power level setting of 1), the heater is energized, or xe2x80x9conxe2x80x9d, for a shorter period of time of each duty cycle as compared to the period of time which the heater is xe2x80x9conxe2x80x9d for each duty cycle at a higher power level setting. Examples of such operation are set forth in U.S. Pat. Nos. 4,816,647 and 4,443,690, which are assigned to the present assignee.
To preserve the life of the glass cooktop, operation of each heater typically is limited to not exceed a preset temperature. For example, with one particular glass cooktop, the temperature of the glass cooking portion of the cooktop is monitored to avoid heating the glass cooking portion to or above 560xc2x0 C. Temperature monitoring is performed by respective resistive temperature devices (RTDs) positioned so that each RTD exhibits a resistance related to the temperature of the cooktop at each heater. If any one RTD exhibits a resistance representative of a temperature at or above 560xc2x0 C., then the associated heater is de-energized or operated at a power level below the selected power level so that the cooktop cools.
Over time, the RTDs and other components associated with heater control may xe2x80x9cdriftxe2x80x9d. The term xe2x80x9cdriftxe2x80x9d, as used herein, refers to a condition in which a determined temperature varies from an actual temperature. Drift can be caused by many different factors, including component degradation or corrosion. For example, an RTD which has not degraded may exhibit a resistance of 1 k ohm at a temperature limit of 560xc2x0 C., whereas an RTD which has degraded may exhibit a resistance of 900 ohms at the same actual temperature. As a result, and rather than limiting operation of the heater to 560xc2x0 C., the degraded RTD may allow operation of the heater to temperatures in excess of 560xc2x0 C. Such drift is not limited to being caused by degradation of an RTD, and can be caused by many different factors.
In another example, the determined temperature may be 560xc2x0 C. when the actual temperature is much lower, e.g., 400xc2x0 C. In such circumstances, the associated heater will be energized, or operated at a lower power level than the user selected power level. Cooking, therefore, may proceed much slower than desired.
In addition, and during operation, a user may change the power level setting to a higher or lower power level than the initial power level setting. For example, a higher power level setting may be desired if cooking is not proceeding as quickly as desired. Similarly, a lower power level setting may be desired if cooking is proceeding too quickly or if an overflow event is imminent. Rapid response by the cooktop system to user initiated changes in power level enhances customer satisfaction with such system.
Although the energization of the heater is immediately altered to correspond to a lower power level upon user selection of such lower power level, due to thermal inertia of the load (i.e., the pot or pan, the food in the pot or pan, and the glass cooktop), the temperature of the load does not immediately decrease to the temperature corresponding to the lower power level. Rather, the temperature of the load gradually decreases to a temperature corresponding to the lower power level setting. More rapidly decreasing the temperature of the load under such conditions would facilitate cooking food more closely in accordance with user preferences.
One known algorithm for operating a cooktop heating element in a fast cool mode is described in U.S. Pat. No. 4,443,690. As explained in the subject patent, a signal representing a power setting lower than the actually selected setting is substituted for the signal representing the selected setting for the duration of the fast cool mode. As further explained in the subject patent, an energy counter is utilized to determine whether the fast cool mode should be implemented based on certain operating conditions. Providing simplified and uncomplicated methods and systems for rapidly cooling a heater, in comparison to the method and system described in U.S. Pat. No. 4,443,690 which involve an energy counter and multiple thresholds, would facilitate implementation of fast cool down operation.
In one aspect, a cooktop system comprising at least one cooktop heater and a controller coupled to the heater and operable to control supply of power to the heater is provided. The cooktop system further comprises a control interface coupled to the controller. The interface comprises a selection unit for operator selection of a power level setting for the heater. The controller is configured to switch off supply of power to the heater if a second power level selection for the heater is a lower power level than a first power level selection. In the example embodiment, the controller is further operable to detect drift.
In another aspect, a method for controlling operation of a cooktop heater is provided. The method, in one example, comprises the steps of supplying power to the heater in accordance with a first power level selection, and upon receipt of a command to reduce the power level from the first power level selection to a second power level selection, switching off supply of power to the heater. In another example, the method includes the step of detecting drift.
In yet another aspect, a controller for coupling to a heater of a cooktop is provided. The controller comprises a processor operable to switch on supply of power to the heater upon receipt of a first command to energize the heater according to a first power level selection, and switch off supply of power to the heater upon receipt of a second command to energize the heater according to a second power level selection. The controller also, in the example embodiment, is operable to detect drift.